US 20110096655A1 (19) United States (12) Patent Application Publication (10) Pub. N0.: US 2011/0096655 A1 MUELLER et al. (43) Pub. Date: Apr. 28, 2011

(54) FORMING LIGHT-TRANSMITTING COVER (60) Provisional application No. 60/781,085, ?led on Mar. LAYER FOR RECORDING MEDIUM 9, 2006.

(75) Inventors: William R. MUELLER, . . . . Bremwood, TN (Us); Ed Publication Classi?cation PICKUTOSKI, Blakely, PA (U S) (51) Int. Cl. GIIB 7/252 (2006.01) (73) Assignee: CINRAM INTERNATIONAL INC,’ Scarborough (CA) (52) US. Cl...... 369/283; G9B/7.171

(21) Appl. No.: 12/965,270 (57) ABSTRACT (22) Filed: Dec‘ 10’ 2010 An optical recording medium includes a recording layer in or . . on a substrate, a light-transmitting cover layer over said Related U's' Apphcatlon Data recording layer, and a disc rib over an outer periphery of a ?rst (63) Continuation-impart of application NO_ 11/715,249, side of the substrate and delimiting an outer diameter of the ?led on Mar. 6, 2007. cover layer. Patent Application Publication Apr. 28, 2011 Sheet 1 0f 4 US 2011/0096655 A1 1 Mold substrate- with information bearing side 511 Fig. 1 Form information layer over S; 3 infcrmation-bearing side of suhstrata

1 Farm saver layer over information layer 515 with disc rib over outer disc'- periphery l Patent Application Publication Apr. 28, 2011 Sheet 2 0f 4 US 2011/0096655 A1

Fig. 2B Patent Application Publication Apr. 28, 2011 Sheet 3 0f 4 US 2011/0096655 A1

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Fig. 2E Patent Application Publication Apr. 28, 2011 Sheet 4 0f 4 US 2011/0096655 A1

m.E EQQMMMHW @EEQU mm

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“238mm m mEHQU mow?m @m mmm miowumw: @362 US 2011/0096655 A1 Apr. 28, 2011

FORMING LIGHT-TRANSMITTING COVER ?lm (of metal or alloy) or the like, to form an information LAYER FOR RECORDING MEDIUM layer. In the case of a CD, a plastic protective coating is applied over the re?ective ?lm, and then art (for example, a CROSS-REFERENCE TO RELATED picture, a design, text, etc.) is typically printed on the upper APPLICATION surface of the disc (that is, on the side of the substrate Which [0001] This application is a continuation-in-part of Us. bears the information layer), to form an end product Which is patent application Ser. No. 11/715,249 ?led Mar. 6, 2007 1.2 mm thick. In the case of DVDs, tWo half-thickness sub Which claims the bene?t of Us. provisional application No. strates (that is, approximately 0.6 mm each) are typically 60/781,085, ?led Mar. 9, 2006. formed, metalliZation is applied to one (for example, DVD-5) or both (for example, DVD-10, DVD-9, DVD-18) half-thick TECHNICAL FIELD ness substrates, and the tWo half-thickness substrates are bonded by an adhesive (for example, hotmelt adhesive, ultra [0002] This application relates to optical storage media. In violet light-cured adhesive, etc.), With the information layer particular, the application relates to a method for forming a being shielded from the external environment by the half thin light-transmitting cover layer over an information layer thickness substrates as cover layers. A second information for an optical recording medium. layer can be formed for a DVD (for example, DVD-18) by applying a photo-polymer coating over a metalliZation layer DESCRIPTION OF RELATED ART applied to a substrate and the second information layer is [0003] Use of CDs (compact discs) and DVDs (digital ver embossed by a stamper into the photo-polymer layer Which is satile discs or digital video discs) as optical storage media then UV cured, metalliZed and protective coated. (“optical disc”) for storing and transporting content (such as [0006] Recordable type optical media typically include a audio, video, graphics, computer software, etc.) in an opti spiral Wobble groove in the substrate. The groove de?nes cally readable manner has beenpopular for a number of years. recording channels on the disc for recording data, provides Several formats of optical discs are currently available, information for tracking of the disc While Writing or reading including (A) read-only formats such as CD-DA (digital data, and has its Wobble frequency modulated to contain audio compact disc), CD-ROM (CD-read-only memory), addressing and other information for the Write and read pro DVD-ROM, and other formats Wherein content is pre-re cesses. The substrate (including information layerbearing the corded on the disc (such as by using an injection molding spiral Wobble groove) can be formed by injection molding, process), and (B) recordable formats in the form of (i) Write using a stamper electroformed With a glass master. In addi once read-many times formats such as CD-R (CD-record tion, recordable-type optical media generally include at least able), and DVDIR (DVD-recordable), etc., or (ii) reWritable a recording layer, and in addition a re?ective layer (of metal or formats such as CD-RW (CD-reWriteable), DVD-RAM alloy) and a protective layer. Information is recorded in the (DVD-Random Access Media), DVD-RW or DVD+RW recordable-type optical medium by directing a laser light DVD-reWriteable) PD (Phase change Dual disk) and other beam modulated by signals to selectively change optical char phase change optical discs. acteristics (re?ectivity or extinction coe?icient) of the record [0004] In conventional read-only type optical discs (for ing layer. The recording layer in Write-once read-many times example, CD-ROM, DVD-ROM, etc.), data is generally optical media typically includes a photosensitive organic dye stored as a series of “pits” embossed in a plane of “lands”. Which is heated during recording to form irreversibly a pat Microscopic pits formed in a surface of a plastic medium [for tern of marks or pits in the recording layer. example, polycarbonate or polymethyl methacrylate [0007] Each recording side of a reWritable disc also uses (PMMA)] are arranged in tracks, conventionally spaced radi multiple layers beginning With a polycarbonate plastic sub ally from the center hub in a spiral track originating at the strate containing a shalloW spiral groove extending from the medium center hub and ending toWard the medium’s outer inside to the outside diameter of the disc.A DVD-RW disc (or rim. The light re?ected from a read-only medium’s surface by a DVD-RAM disc) may additionally inside the groove itself. an optical disc player or reader varies according to the pres The substrates (including information layer bearing the spiral ence or absence of pits along the information track. A photo groove, land pre-pits and embossed areas) may be formed by detector and other electronics inside the optical disc player injection molding, using a stamper electroformed With a glass translate the signal from the transition points betWeen these master. Next in the multiple layers of a reWritable disc typi pits and lands caused by this variation into the 0s and 1s of the cally comes a dielectric layer, folloWed by a phase-change digital code representing the stored information. type recording layer having a polycrystalline structure, [0005] Read-only type optical discs generally are produced another dielectric layer and a re?ective layer (of metal or by an injection molding process. Initially, data representing alloy). Additional layers may also be incorporated above or the content to be recorded, encoded as a run length limited beloW the dielectric layer, With a protective coating being digital code (commonly knoWn as an EFM signal in CD applied as a last layer in single-sided optical media. During manufacturing) Which contains its digital information in the recording of the reWritable optical medium, the laser selec timing betWeen transitions, is used to control a laser beam tively heats tiny areas of the recording track to change the recorder to form pits in a photoresist or a dye-polymer layer phase of each heated area from more crystalline into less on an optical grade glass disc knoWn as a glass master in a crystalline (also knoWn as “amorphous”) phase, in order to mastering process. A metalliZed glass master is used in an create marks that can be called “pits” (the term “pit” is used electroforming process to form (typically, metal) stampers. A broadly herein to cover, for example, a pit in a read-only type stamper is used on one side of an injection molding cavity to optical disc, and a pit or mark in a recordable or reWritable emboss a layer of pits and lands on a transparent polymer optical disc). During erase, the laser (in a process called substrate formed by injection molding. The information bear “annealing”) changes the amorphous areas back into more ing surface of the substrate is then covered With a re?ective crystalline areas. US 2011/0096655 A1 Apr. 28, 2011

[0008] Some exemplary optical disc manufacturing tech the light-transmitting property of the cover layer. In addition, niques (including methods, systems and apparatuses) are dis spin coating techniques typically apply much more resin than cussed in US. Pat. Nos. 5,181,081, 5,315,107, 5,766,495, is required to form the 0.1 mm cover layer, and the excess 5,792,538, 5,900,098, 5,932,042, 5,932,051, 5,932,058, must be collected to avoid Waste. 5,935,673, 5,949,752, 5,958,651, 5,995,481, 5,997,976, [0016] There is a need for improved techniques for forming 6,117,284, 6,124,011, 6,160,787, 6,309,496, 6,309,727, a light-transmitting cover layer Which does not have the limi 6,361,845, 6,440,248, 6,527,538, 6,726,973 and 6,896,829, tations described above. Which are incorporated by reference herein in their entireties in order to more fully describe the state of the art as of the date SUMMARY of the subject matter described and claimed herein. Addi [0017] This disclosure describes a method for manufactur tional exemplary techniques are discussed in US. Pat. Nos. ing an optical recording medium that includes a recording 4,995,799, 5,766,359, 5,800,687, 5,863,328, 5,863,399, layer in or on a substrate, a light-transmitting cover layer over 5,913,653, 6,261,403, 6,368,435 and 6,814,825, Which are said recording layer, and a disc rib over an outer periphery of also incorporated by reference herein in their entireties. a ?rst side of the substrate and delimiting an outer diameter of [0009] Optical disc players for optical discs Which conform the cover layer. With one of the CD or DVD formats use a red laser (With a Wavelength range of 635 nm to 660 nm in the case of DVD BRIEF DESCRIPTION OF THE DRAWINGS and a Wavelength of approximately 780 nm in the case of CD). [0018] The features of the present application can be more [0010] Optical discs using a blue laser (With a Wavelength readily understood from the folloWing detailed description range of 400 nm to 420 nm) have also been introduced, such With reference to the accompanying draWings Wherein: as HD DVD and BD (each of Which includes read-only, [0019] FIG. 1 shoWs a How chart illustrating a method for recordable and reWritable formats). The popularity of optical manufacturing an optical recording medium, according to an storage media driven by advancements in computer, informa exemplary embodiment of the present disclosure; tion communication and multimedia technologies has been [0020] FIG. 2A shoWs a plan vieW of an optical recording accompanied also by demands for a higher density and a disc, according to an exemplary embodiment; greater capacity of optical storage media. HD DVD and BD [0021] FIG. 2B shoWs a sectional vieW of the optical provide high density formats Which attempt to meet such recording disc cut along the line AA' shoWn in FIG. 2A; demands. [0022] FIG. 2C shoWs an exploded, notional vieW along a [0011] HD-DVD format discs can be replicated using a track direction of section B in FIG. 2B; process similar to the process for forming a DVD disc, except [0023] FIG. 2D shoWs an exploded vieW of an end portion that the minimum pit length is shorter and therefore the laser of an optical recording medium Which includes a disc rib; beam recorder used in the mastering process must be adapted [0024] FIG. 2E shoWs an exploded vieW of an end portion to form the shorter pits. of a holographic storage medium Which includes a disc rib; [0012] BD format discs have a substantially different struc [0025] FIG. 3 shoWs a schematic diagram illustrating a ture than HD-DVD, DVD and CD discs. For HD-DVD, DVD system for manufacturing optical recording media. and CD discs, each information layer is closer to the middle of the disc than the surface of the disc. In contrast, the informa DETAILED DESCRIPTION tion layer in the BD format disc is separated from the surface [0026] Methods for manufacturing an optical recording of the disc only by a 0.1 mm transparent cover layer. medium, including in particular improved techniques for [0013] A number of techniques have been proposed for forming a light-transmitting cover layer (such as for a BD disc forming the 0.1 mm cover layer on the information layer for or a holographic medium) of a speci?ed thickness, are dis the BD disc. cussed herein. [0014] For example, the cover layer may be a disc-shape [0027] In describing examples and exemplary embodi punch-out from a thin-layer plastic sheet. The disc-shape ments, speci?c terminology is employed for the sake of clar plastic punch-out is then bonded on the information layer, and ity in this disclosure. HoWever, the disclosure of this patent therefore needs to have precise dimensions to cover the infor speci?cation is not intended to be limited to the speci?c mation layer. The plastic sheet may be a laminate sheet con terminology so selected and it is to be understood that each stituted by an adhesive sheet having a predetermined form speci?c element includes all technical equivalents that oper Which is laminated onto a release sheet and Wound into a roll. ate in a similar manner. See, for example, US. Patent Application Publication No. [0028] A method for manufacturing an optical recording US2005/0109454A1. HoWever, such plastic sheets substan medium, in an example (FIG. 1) of this disclosure, includes tially increase the cost of manufacture of the disc. molding a substrate including an information bearing side [0015] A number of spin coating techniques and appara (step S11), forming an information layer by applying a re?ec tuses have been proposed for depositing a resinous material to tive layer over the information-bearing side of the substrate form the cover layer on the information layer. See, for (step S13), and forming a light-transmitting cover layer over example, US. Patent Applications Publications Nos. the information layer by depositing a liquid resin on the US2005/0039675A1, US2005/0042371A1, US2005/ information layer (step S15). A disc rib is formed an outer 0053728A1, US2005/0175771A1 and US2005/0281179A1. periphery of the information bearing side of the substrate, to HoWever, effective use of spin coating to form the cover layer stop How of the deposited resin beyond the outer disc periph has been very dif?cult. For example, controlling the thickness ery Some additional examples of the method are discussed of the cover layer formed through spin coating has been infra. problematic. Further, spin coating is a turbulent activity and [0029] The volume of the liquid resin that is deposited can therefore may result in bubbles in the cover layer Which affect be predetermined based on a desired thickness of the cover US 2011/0096655 Al Apr. 28, 2011

layer. For example, an approximation of the required volume US2005/0072336A1, US2005/0112319A1 and US2005/ of the resin for a disc having a radius of 6 cm, an inner 0158504A1, the entire disclosures of Which are incorporated clamping area With a radius of 1 cm and a cover layer thick by reference herein. ness of 0.1 mm is approximately 1.1 cm3 Which can be deter [0037] The substrate 21 and the information layer 23 in mined as follows: combination With the cover layer 22 and the protective hard coat 24 may comply With the requirements of, for example, a (layer thickness)-n- [(disc radius)2—(inner radius)2]. BD read-only disc. For such a disc, the information layer 23 [0030] In the example of a BD disc, a light-transmitting includes a series of pits embossed in a plane of land (by a cover layer With a thickness of 0.1 mm is required With a stamper in the injection molding process), all of Which being tolerance of 10.003 mm. Therefore, an approximation of the covered by the re?ective layer 23a. In addition, the informa volume ofresin to be dispensed is 1.1 cm3:0.011 cm3. tion layer 23 comprises an information track having pits With a minimum length along the track in a range of 138 nm to 160 [0031] Accordingly, the desired light-transmitting cover nm. The information layer can comprise information marks layer for a disc can be formed by discharging a suitable con?gured for reading using a laser With a Wavelength in a volumetric amount of resin over the information layer, and range of 400 nm to 420 nm and a numerical aperture of0.85, controlling the ?oW to obtain relative ?atness of the disc. and can have information capacity of 23 GBytes or more. [0032] An example of an optical recording disc Which can [0038] The disc can include one information (or recording) be manufactured in accordance With this disclosure is shoWn layer (FIG. 2C) or multiple information (or recording) layers exemplarily in FIGS. 2A through 2C. An optical recording (not shoWn). In the case of the disc having tWo information disc 20 comprises a substrate 21 (With information bearing layers, the upper information layer (that is, closer to the side 2111), an information (or recording) layer 23 including a light-transmitting cover layer) is covered by a semi-re?ective re?ective layer 2311 over the information bearing side 2111 of layer (for example, gold, silicon, silver, alloy, etc.) and the the substrate 21 and a light-transmitting cover layer 22. The loWer information layer (that is, further from the cover layer) cover layer 21 has a thickness of approximately 0.1 mm. The is covered by a re?ective layer (for example, aluminum, etc.). optical recording disc 20 has a thickness in a range of 0.9 mm Techniques for forming multi-layer discs (that is, both infor mation layers being readable from the same disc side) are to 1.4 mm. Well-understood. See, for example, US. Pat. No. 6,117,284 [0033] The substrate 21 is preferably injection molded and US. Patent Application Publications Nos. US2005/ from a material used conventionally for optical disc sub 0002018A1 and US2005/0072518A1 the entire disclosures strates, such as polycarbonate resins, acrylic resins (for of Which are incorporated by reference herein. example, polymethyl methacrylate, i.e. PMMA), polyole?ne [0039] The optical recording medium 10 can be single resins, or the like. Since the substrate does not need to be sided or double-sided. See, for example, commonly-oWned optically transparent (because a laser beam is incident US. Pat. No. 7,684,309, the entire content of Which are incor through the cover layer), the substrate may alternatively be porated by reference herein. made of another plastic material, glass, ceramics, and the like. [0040] It has been determined through experimentation that HoWever, if the substrate is formed through injection mold the deposited resin preferably has a viscosity of 10 mPa*s or ing, the material of the substrate is preferably one suitable for less, to alloW the liquid resin to ?oW in a desired manner to injection molding. form a substantially uniform thickness. For many resins, the [0034] The re?ective layer 2311 can be deposited by a sput desired viscosity is achieved by applying heat. tering process on the information-bearing side of the sub [0041] For example, the method for forming the light-trans strate 21. A material of the re?ective layer may include a mitting cover layer may further include applying a predeter metallic element, semi-metallic element, semiconductor ele mined amount of heat locally to the deposited resin or a region ment, or a composite thereof. Suitable materials for the surrounding the deposited resin, for a predetermined duration re?ective layer include Al, Au, Ag, Cu, Ni, In, Ti, Cr, Pt, Si, of time, to cause the deposited resin to ?oW over the substrate, alloy, etc. The re?ective layer is preferably a thin ?lm having and then removing the heat and alloWing the resin to form the a thickness of 5 nm to 200 nm. cover layer. The amount of applied heat preferably causes a [0035] The resin that is used to form the light-transmitting viscosity of the resin to drop to 10 mPa*s or less. cover layer 22 can include polycarbonate, an ultraviolet cur [0042] In another example, the method for forming a light able resin (such as the type that can be used as an adhesive to transmitting cover layer includes heating the resin to a pre bond a layer to a substrate or to another layer in an optical determined temperature such that the heated resin has a vis disc), an electron ray curable resin or another radiation cur cosity of 10 mpa*s or less, and then the heated resin having able resin. The light transmitting layer formed With such a the viscosity of 10 mpa*s or less is applied on the information resin should be optically transparent, exhibit loW optical layer. absorption or re?ection in the laser Wavelength range to be [0043] Some liquid resins have a su?iciently loW viscosity used, and have loW birefringence. that alloWs the resin to ?oW beyond the outer disc periphery, [0036] A protective hard coat 24 Which has properties of if unimpeded. Therefore, a disc rib is formed over an outer scratch resistance and abrasion resistance preferably covers periphery of the information bearing side of the substrate, to the cover layer 22. The hard coat may be formed on the cover stop ?oW of the deposited resin beyond the outer disc periph layer by applying a hardcoat agent composition (for example, ery (for example, disc rib 21b in FIG. 2A and in FIG. 2D). For UV hardening resin) on the cover layer, folloWed by curing example, the disc rib may be formed along With the substrate through irradiation With active energy rays such as ultraviolet in the molding stage (and may be the same material as the rays, electron rays or visible rays. Examples of a hardcoat substrate). In another example, the disc rib may be a portion composition and techniques for applying the composition are of the cover layer forming apparatus Which is placed above described in US. Patent Application Publications Nos. the substrate before the liquid resin is applied. US 2011/0096655 A1 Apr. 28, 2011

[0044] In addition, maintaining the disc at a level With Zero broad sense to cover any recording medium including a pitch When the liquid resin is deposited helps to attain a recording layer Wherein information recorded therein can be substantially uniform thickness of the cover layer. In this reproduced by applying an optical beam and detecting a beam regard, the method for forming the cover layer may further re?ected or passed through the recording layer. include applying a vacuum from beloW the substrate. The [0049] For example, embodiments are described With ref vacuum is preferably applied before the liquid resin is depos erence to read-only format discs as examples. It should be ited on the substrate and is maintained until the resin solidi apparent after a reading of this disclosure, hoWever, that the ?es. techniques of this disclosure apply similarly to recordable (Write once read many times) and reWritable format discs. [0045] An example of a system for manufacturing the opti [0050] As another example, the techniques of this disclo cal recording media of this disclosure Will be described With sure can be applied to form a cover layer (such as in FIG. 2E) reference to FIG. 3. as or in a surface of a holographic medium (e.g., a recording [0046] In system 30 an injection molding station 31 injects layer 123 betWeen substrate 21 and cover layer 22, such as a molten transparent polycarbonate plastic into a mold cavity, made of plastic). Other examples of such holographic storage having a stamper on one face to produce a clear plastic disc or recording medium are disclosed in U.S. PatentApplication With pits impressed on one side. The mold cavity is con?g Publication No. US2007/0242589A1 and US2008/ ured to alloW a disc rib to be formed above the outer edge of 0100890A1, the entire contents of Which are incorporated the substrate. The molded disc is placed by a robotic arm 32a herein by reference. in a carousel 35 Which rotates to bring the disc to the metal [0051] The examples and exemplary embodiments above liZation station 33. A robotic arm 32b then lifts the disc and are illustrative, and many variations can be introduced on brings it into the metalliZation station. The metalliZation sta them Without departing from the spirit of the disclosure or tion 33 applies a re?ective metal layer coated upon the pitted from the scope of the appended claims. For example, ele surface of the disc, and then the disc is returned to the carousel ments and/or features of different illustrative and exemplary 35. The disc travels upon disc transport belt 34 during Which embodiments herein may be combined With each other and/ or time it cools someWhat. The disc is moved by a robotic arm substituted for each other Within the scope of this disclosure. (not shoWn) from the transport belt 34 to a coating station 36. [0052] This application is a continuation-in-part of U.S. [0047] At the coating station 36, a 0.1 mm light-transmit patent application Ser. No. 11/715,249 ?led Mar. 6, 2007 ting cover layer is formed on the disc by depositing a prede Which claims the bene?t of U.S. provisional application No. termined volume (approximately 1.1 cm3) of liquid resin onto 60/781,085, ?led Mar. 9, 2006, the entire disclosures ofWhich the surface of the disc, under a heated environment to bring are incorporated by reference herein. the liquid resin to a viscosity of 10 mPa*s or less. Thereafter, What is claimed is: the resin is alloWed to solidify. Next, the disc is lifted by a 1. An optical recording medium comprising: robotic arm 320 to a curing station 37 Where the disc is a substrate including a ?rst side; exposed to su?icient ultra-violet light to cure the resin. Fol a recording layer in or on said substrate; loWing curing, the disc is transported to a coating station 39 a light-transmitting cover layer over said recording layer; Where a protective hardcoat is applied. and [0048] The techniques of this disclosure can be applied in a disc rib over an outer periphery of said ?rst side of said any of many contexts for forming a thin light-transmitting substrate and delimiting an outer diameter of said light cover layer over an information (or recording) layer for an transmitting cover layer. optical recording medium, and the term “optical recording medium” and “optical recording media” are used herein in a * * * * *